On Wed, 2023-02-15 at 22:08 -0600, Ron wrote: > On 2/15/23 21:45, Laurenz Albe wrote: > > On Wed, 2023-02-15 at 10:20 -0600, Ron wrote: > > > On 2/15/23 02:46, Laurenz Albe wrote: > > > > Both are the same. > > > > There is an old myth that says that you should use the more selective column first > > > > (which would be "code"), but that is just a myth. > > > > > > Only on Postgresql? > > > > No, on all relational databases that use B-tree indexes. > > Not only is "all" is a very absolute word (I know of a counter-example), but > querying on the second segment means that you have to scan the whole tree > instead of isolating one sub-branch. The question was about a multi-column index where all columns are compared with "equal" in the WHERE condition. For other cases, order matters. I am aware of the danger of absolute claims, but as far as I can tell, this is in the nature of B-tree indexes. Yours, Laurenz Albe
